Pass by Reference

Reduces copying
 int  sum(std::vector<int>  &v)  {
     int  result  =  0;
     for  (std::vector<int>::size_type  i  =  0;
                         i  !=  v.size();  ++i)
         result  +=  v[i];
     return  result;
 }
Modifying argument also modifies the original